In the printing industry, a variety of screens and masks and other materials are created by applying a material to a substrate in a desired pattern and then exposing the material and the substrate to ultraviolet light radiation to cross-link the polymers in the material and thereby cure the material and secure it to the substrate. For the purposes of this application, the example of screens for silk screening and screen printing processes will be used. But, it is to be understood that the curing processes disclosed herein can be applied to many other printing industry curing needs.
According to common practice in the industry, various exposure systems are used. An exposure system generally includes an enclosure, a transparent, transmissive or translucent platen and an opaque cover which also often includes a device for securing the screen to the platen during exposure process. The enclosure includes a source of electromagnetic radiation that produces electromagnetic radiation of the desired wavelength. Commonly, electromagnetic radiation is used in the ultraviolet wavelengths. Commonly, illumination of these systems is provided by high intensity lamps such as metal halide lamps. Metal halide lamps produce a broad light spectrum including the ultraviolet spectrum. Besides the useful ultraviolet spectrum, metal halide lamps also produce a great deal of waste light, the waste light being the portion of the broad light spectrum that is not useful in the exposure process. This waste light represents a substantial waste of energy. It is not uncommon for screen light exposure systems to draw amounts of energy up to 6 kW. Generally because of their high power draw requirements metal halide lamp systems must be coupled to a 220 volt circuit to accommodate their power needs.
In addition, metal halide lamps produce large amounts of waste heat which must be dissipated. Accordingly, the systems often have complicated cooling systems. Some systems are cooled by cooling fans which must be continuously monitored to control lamp temperature and to prevent excess heat exposure from damaging the emulsion screens and substrates. To prevent excess heat exposure, some systems use water cooling arrangements in order to dissipate the great amount of excess heat produced.
Another issue is that lamps of the prior art, such as metal halide lamps, gradually change their emission qualities over time. Thus, in order to operate and provide accurate exposures, these systems often require computerized programmable exposure control systems to compensate for variations in lamp emission and energy output. Often these exposure control systems are relatively complicated in order to maintain a level of ultraviolet lighting exposure in the desired wavelengths to properly cure emulsions.
In addition, high intensity metal halide or mercury lamps typically have a given period of time during which the lamp is warming up or coming up to temperature. During this warm up period the light spectrum produced is relatively unpredictable, thus causing variations in the amount of light exposure to the emulsion over time.
In addition, metal halide lamps and the other lamps commonly used have a limited use of life, typical lamp life spans range from tens to hundreds of hours. Accordingly, metal halide lamps or other lamps must be replaced on a regular basis. These lamps are relatively expensive and their replacements must be budgeted for.
Another issue is that metal halide lamps and other lamps used in the exposure process often include hazardous waste in the form of heavy metals, such as lead and mercury, and require proper disposal to prevent releasing these heavy metals and other toxins into the environment. Mercury lamps in particular are a problem for disposal.
Accordingly, there is room for improvement in printing industry screen exposure systems. What is needed is a screen exposure system which is less wasteful of energy, does not require specialized electrical circuitry and power requirements to operate, does not produce large amounts of excess heat, does not require large and cumbersome computerized programmable exposure control systems to control, does not have extensive warm up periods with an unpredictable spectrum output, has lamps with relatively long life spans, and does not pose a hazardous waste threat to the environment when disposed of.